全文获取类型
收费全文 | 206242篇 |
免费 | 11482篇 |
国内免费 | 5707篇 |
专业分类
电工技术 | 8036篇 |
技术理论 | 10篇 |
综合类 | 10087篇 |
化学工业 | 31816篇 |
金属工艺 | 11693篇 |
机械仪表 | 11233篇 |
建筑科学 | 11401篇 |
矿业工程 | 4640篇 |
能源动力 | 4897篇 |
轻工业 | 11861篇 |
水利工程 | 3375篇 |
石油天然气 | 8273篇 |
武器工业 | 997篇 |
无线电 | 22506篇 |
一般工业技术 | 31193篇 |
冶金工业 | 8988篇 |
原子能技术 | 1774篇 |
自动化技术 | 40651篇 |
出版年
2024年 | 550篇 |
2023年 | 2152篇 |
2022年 | 3685篇 |
2021年 | 5134篇 |
2020年 | 3886篇 |
2019年 | 3438篇 |
2018年 | 17732篇 |
2017年 | 17134篇 |
2016年 | 13341篇 |
2015年 | 5491篇 |
2014年 | 6440篇 |
2013年 | 7644篇 |
2012年 | 11144篇 |
2011年 | 17893篇 |
2010年 | 15641篇 |
2009年 | 12575篇 |
2008年 | 13530篇 |
2007年 | 14215篇 |
2006年 | 6636篇 |
2005年 | 6914篇 |
2004年 | 5109篇 |
2003年 | 4828篇 |
2002年 | 4047篇 |
2001年 | 3192篇 |
2000年 | 3136篇 |
1999年 | 3227篇 |
1998年 | 2571篇 |
1997年 | 2067篇 |
1996年 | 2019篇 |
1995年 | 1694篇 |
1994年 | 1326篇 |
1993年 | 1025篇 |
1992年 | 797篇 |
1991年 | 619篇 |
1990年 | 465篇 |
1989年 | 339篇 |
1988年 | 331篇 |
1987年 | 189篇 |
1986年 | 177篇 |
1985年 | 123篇 |
1984年 | 89篇 |
1983年 | 56篇 |
1982年 | 55篇 |
1968年 | 46篇 |
1967年 | 37篇 |
1966年 | 42篇 |
1965年 | 46篇 |
1958年 | 37篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
During the last ten years, techniques have been developed to measure the distribution of grain boundaries in polycrystals
as a function of both lattice misorientation and grain boundary plane orientation. This paper presents a brief overview of
the techniques used for these measurements and the principle findings of studies implementing these techniques. The most significant
findings are that grain boundary plane distributions are anisotropic, that they are scale invariant during normal grain growth,
that the most common grain boundary planes are those with low surface energies, that the grain boundary populations are inversely
correlated with the grain boundary energy, and that the coincident site lattice number is a poor predictor of the grain boundary
energy and population. 相似文献
993.
Some months ago the submarine Nautilus was in dock for refueling. It had traveled 60,000 miles, but the total uranium used would make a lump smaller than a light bulb. This is only one example that the Atomic Age is here with us, now! How and where does this incredible Atomic Age challenge the first and greatest of America’s basic industries? 相似文献
994.
关于中国加入WTO以后,如何适应新的形势和面对新的竞争,从而构建新的影视高等教育体系?本文从以下三个方面进行了论述:21世纪是彩色读图时代,影视知识技术是人才所必备的三大基本知识技术之一;中国的影视教育必须构建学历教育、职业技能教育和成人继续教育相结合的国民教育体系以及四合一的教育教学模式和产学研相结合的人才培养体制及其运行机制。 相似文献
995.
消失模涂料对EPS裂解产物传输特性的影响 总被引:1,自引:0,他引:1
针对消失模铸造过程中EPS模样裂解产物,涂料性能对铸件质量的影响,介绍了一种消失模涂料对EPS裂解产物传输特性的测试仪器吸测试方法。讨论了消失模涂料厚度、涂层高温透气率、涂料组分对EPS裂解产物传输特性的影响。 相似文献
996.
将9SiCr钢的粒状原始组织改变为片状,再经830℃淬火后,其马氏体形态为筐篮编结状。而传统工艺所获得的马氏体形态为针状.这种筐篮编结状马氏体是9SiCr钢中一种崭新的组织形态,其精细结构为平行成束的板条。亚结构为高密度缠结位错.它有良好的综合机械性能,强韧性高,耐磨性高。 相似文献
997.
Biaxial forming behavior is investigated for three aluminum sheet alloys (Al 5182 containing 1% Mn (5182+Mn), Al 5754, and
6111-T4) using a heated die and punch in the warm forming temperature range of 200–350 °C. It is found that, while all three
alloys exhibit significant improvement in their formability compared with that at room temperature, the non-heat-treatable
alloys 5182 + Mn and 5754 give higher part depths than that of heat-treatable 6111-T4. The formability generally increases
with decreasing BHP (BHP), but increasing the forming temperature and/or BHP minimizes the wrinkling tendency and improves
the forming performance. The stretchability of the sheet alloys increase with increasing temperature and increasing BHP. For
the alloys and forming conditions involved in the current study, the formability, measured in terms of part depth, comes mainly
from the drawing of metal into the die cavity, although stretching effects do influence the overall forming behavior. The
optimum formability is achieved by setting the die temperature 50 °C higher than the punch temperature to enhance the drawing
component. Setting the die temperature higher than the punch temperature also improves the strain distribution in a part in
such a manner that postpones necking and fracture by altering the location of greatest thinning. 相似文献
998.
各向异性Sm2Fe17Nx磁粉的结构与磁性能 总被引:11,自引:1,他引:11
研究了Sm2Fe12Nx磁粉的制备、结构与磁性能,发现Sm—Fe合金的铸态组织主要由Sm2Fe17、α—Fe和SmFe2三种物相组成,而经过1000℃均匀化退火48h处理后富Sm的SmFe2相基本消失,α—Fe相的品粒变小,数量减少。随着氯化时间延长到10h,Sm2Fe17相始终未改变其Th2Zn17型结构,而氯原子浓度增加,所有的X射线衍射峰均向小角度方向移动;但在氮化时间超过10h后,物相要发生变化,导致磁性能降低。在500℃下流动的氮气氛中对Sm2Fe17合金氮化2、4、6、10h未加磁场取向的磁粉中,以氮化6h的磁性能值最高:σr=35.44Am^2/kg(emu/g),Hc=58kA/m(729.03Oe)。磁性能值偏低的原因与测量磁场较低,粒径分布不均匀及粒径较大有关。 相似文献
999.
Jung-Chel Chang Cheol Choi Jae-Chul Kim Young-Hoon Yun 《Journal of Materials Engineering and Performance》2003,12(4):420-425
Effects of the hot-isostatic pressing (HIP) process on microstructures and mechanical properties of Ni-base single crystal
superalloy CMSX-4 were investigated. In the overall heat treatment process, the HIP treatment remarkably induced the healing
behavior of micropores and decreased the pore size and porosity of superalloy CMSX-4 compared with normally treated specimens.
The microstructure of γ′ phase after the HIP process showed rather a coarsening tendency and could be developed by the partially solution and aging
treatment. Consequently, the elimination of cast micropores using the HIP step resulted in the inhibition of crack initiation
in microstructure and improved the stress-rupture lives of Ni-base single crystal superalloy by 185%. 相似文献
1000.
Phosphorus was added to Fe-50 wt.% Ni in the form of a coated composite powder via an electroless plating process. Addition
of phosphorus to Fe-50 wt.% Ni facilitated increases in density and grain size, both of which were beneficial to magnetic
performance. Because of the homogeneous distribution of phosphorus in the powder, the optimal phosphorus addition was much
lower than for those using Fe3P as the phosphorus precursor. The optimal phosphorus addition was close to its maximum solubility in Fe-50 wt.% Ni (about
0.5 wt.%), above which precipitation of excessive phosphorus in the form of iron nickel phosphide, (Fe,Ni)3P, effectively degraded the magnetic properties of Fe-50 wt.% Ni. Without the addition of phosphorus, good magnetic properties
could be achieved only when the sintering temperature was high enough (>1200 °C) to result in a high sintered density and
large grains in the sintered structure. 相似文献